Conventionally, penta-band antennas, which satisfy both a global system for mobile communications (GSM) quad band and a W2100 band, have been used for various communication apparatuses. An example of conventional antennas that satisfy the above-described characteristics will now be described.
FIG. 1 illustrates a conventional inverted F-type antenna 100 including a carrier 110 and a radiator 120. Since the antenna 100 is an inverted F-type antenna, a portion of the radiator 120 becomes a power feeding terminal 121 and a ground terminal 122. The power feeding terminal 121 is connected to a power feeding unit of a communication apparatus, and a ground terminal 122 is connected to a ground surface of the communication apparatus. The antenna 100 shown in FIG. 1 operates in a service band, namely, a GSM quad band and a W2100 band. In terms of frequency, it can be seen that the antenna 100 shown in FIG. 1 operates in a frequency band of about 824 MHz to about 960 MHz and a frequency band of about 1710 MHz to about 2170 MHz.
However, the introduction of an antenna that can satisfy both a GSM quad band and a W2100 band, and can also operate in a long-term evolution (LTE) band, has recently become needed. In particular, the design of an antenna whose operation band expands to an LTE 13 band of about 746 MHz to about 787 MHz is required. However, it is not easy to design a small-sized antenna having a size of about λ/4 or less to satisfy all the above-described service bands, because the following problems arise.
First, bandwidth increase and gain increase of an antenna are contrary to size reduction of the antenna. That is, it is very difficult to increase the bandwidth and gain of an antenna while also making it small. This is a problem because there is demand on the market for simultaneously reducing the size and increasing the bandwidth and gain of antennas.
Second, downsizing of antennas is problematic because it is difficult to cause resonance in a low-frequency band. A resonance frequency depends on the size of the antenna. As the resonance frequency becomes lower, the size of the antenna necessarily increases. Accordingly, when designing an antenna that operates in a frequency band lower than a GSM quad band, such as an LTE 13 band, the size of the antenna necessarily increases. Accordingly, it is difficult to embody a small-sized antenna.
Third, when a service band of an antenna partially expands, a conventionally designed antenna cannot be utilized as is. In other words, according to conventional art, an antenna designed to satisfy a GSM quad band and a W2100 band can be neither utilized as is nor designed to operate even in an LTE 13 band. Accordingly, expansion or change of a service band necessarily involves redesigning the antenna. However, when an antenna is redesigned from the beginning, since a conventionally designed antenna cannot be used as is, previously invested effort and capital cannot be utilized.